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Abstract

The establishment and intensive management of forests for the production of timber
can have significant effects on the soil carbon dynamics. The establishment of forest
on organic soils under grasslands may lead to substantial losses in soil carbon, due to
the site preparation for the planting of trees and other disturbances. This is gradually
compensated by carbon accumulation in tree biomass as the forest grows until
clearfelling at maturity may initiate another substantial carbon loss.
This study had two main aims. The first was to investigate the long-term effects of
forest establishment on natural grassland as well as clearfelling and re-growth of the
forest during second rotation, by looking at the changes in soil carbon stocks and soil
carbon balance in a Sitka spruce (Picea sitchsensis) in Harwood (N. E. England).
Secondly, to investigate the short-term effects of forest clearfelling on the fluxes of
soil CO2, N2O and CH4 and on the environmental factors (soil temperature, water
content and water table depth) affecting them. The fluxes were initially measured in
two mature stands (40-years old) during one growth season. One of the two stands
was subsequently clearfelled while the other was kept intact and fluxes were
measured for a further ten months after clearfelling. The relationships between these
fluxes and the environmental factors were also examined.
The study also investigated the spatial variability of soil CO2 emissions using
geostatistical approaches. The soil CO2 fluxes were measured with two methods, a
closed dynamic chamber and a closed static chamber, giving the opportunity to
compare their relative performance. A performance further investigation on this
discrepancy between the two methods took place in lab experiments and on a soil
monolith, excavated from the 40-year old stand and kept under controlled conditions
in the greenhouse.